The present invention relates to an image observation apparatus such as a head-mounted display (HMD) which introduces light fluxes from plural image-forming elements to an eye of an observer to enable observation of an image.
Observation optical systems used for the HMD and the like are desired to be compact. The observation optical systems are also desired to be capable of providing an image with a wide viewing angle to increase realistic sensation.
A large display element (image-forming element) is preferable to enable the observation optical system to provide an image with a wide viewing angle. However, it is difficult to always obtain display elements having a suitable display area size for required specifications on a display viewing angle of the observation optical system.
U.S. Pat. Nos. 5,982,343 and 6,008,778 and Japanese Patent Laid-Open No. 11-326820 have disclosed observation optical systems that achieve desired wide viewing angle display while using a display element having a smaller display area size compared to a desired display viewing angle. These optical systems enable observation of one image produced by combining plural original images that are displayed on plural display elements and correspond to different viewing fields.
The observation optical system disclosed in U.S. Pat. No. 5,982,343 is provided with a V-shaped mirror. The V-shaped mirror reflects at its one reflective surface light from an original image displayed on a display element toward a pupil and reflects at its other reflective surface light from another original image displayed on another display element toward the pupil.
The observation optical system disclosed in U.S. Pat. No. 6,008,778 is provided with a prism having a symmetric shape with respect to a section including the center of the viewing field for one image produced by combining two original images displayed on two display elements. This observation optical system uses two entrance surfaces of the prism each facing one display element as two reflective surfaces each reflecting light from the other display element.
The observation optical system disclosed in Japanese Patent Laid-Open No. 11-326820 is also provided with a prism having a symmetric shape with respect to a section including the center of the viewing field for one image produced by combining two original images displayed on two display elements. Light from one original image displayed on one display element enters the prism from an entrance surface facing the one display element, is totally reflected by a transmissive/totally reflective surface, is reflected by a reflective surface, and then is transmitted through the transmissive/totally reflective surface toward a pupil. Similarly, light from the other original image displayed on the other display element enters the prism from another entrance surface facing the other display element, is totally reflected by the transmissive/ totally reflective surface, is reflected by another reflective surface, and then is transmitted through the transmissive/ totally reflective surface toward the pupil.
The two reflective surfaces combining the light from the one original image and the light from the other original image and causing them to proceed toward the same pupil are disposed adjacent to each other.
Each of the observation optical systems disclosed in the above patent documents combines the light fluxes from the two display elements at the two reflective surfaces disposed adjacent to each other. Specifically, the light flux from one original image displayed on one display element is reflected by one reflective surface toward the pupil, and the light flux from the other original image displayed on the other display element is reflected by the other reflective surface adjacent to the one reflective surface toward the pupil.
In other words, when considering two optical paths toward the two display elements in backward ray tracing from the pupil, the optical path from the pupil is separated into two optical paths toward the two display elements by the two reflective surfaces disposed adjacent to each other.
These observation optical systems can provide a wider viewing angle than that normally obtained by using a display element having a small display area size. Moreover, they can provide a similar viewing angle to a conventional one by using a more compact optical system (optical system thin in a view axis direction).
However, these observation optical systems include a joint line between the two reflective surfaces that separate the optical path from the pupil into the optical paths toward the display elements in the backward ray tracing. The joint line portion may scatter light to cause flare or the like.